In this sequence of event the lichens functioned as?

In this sequence of events, the lichens functioned as bioindicators of environmental health, signaling changes in air quality and ecosystem stability. Their sensitivity to pollutants, particularly sulfur dioxide and heavy metals, allows them to reflect the levels of environmental stress. Additionally, lichens play a crucial role in soil formation and nutrient cycling, contributing to the overall ecology of their habitats. Thus, they serve both as indicators of environmental conditions and as essential components of their ecosystems.